1. Field of the Invention
The invention relates generally to the field of voltage variable capacitors. More particularly, the invention relates to a hybrid voltage variable capacitor.
2. Discussion of the Related Art
A voltage-controlled oscillator (VCO) is a circuit that generates an oscillating signal at a frequency proportional to an externally applied control voltage. These types of circuits find several applications in telecommunications and are useful for tracking and matching signal frequencies as they shift due to thermal variations, power supply fluctuations, and other sources of frequency shifts.
Metal-oxide semiconductor (MOS) capacitors, also known in the art as voltage variable capacitors (VVCs), have been used in tank circuits of VCOs because of their high quality and good capacitance variation versus tuning voltage characteristics.
Capacitance variation range is an important consideration in VCO circuit design. Typically, the capacitance variation range of a MOS capacitor starts from a flat-band voltage to a threshold voltage, which may be less than 0.7 volts. Beyond this range, the MOS capacitor tuning (or control) voltage does not cause frequency change in the VCO. A narrow capacitance variation range results in a narrow VCO frequency range.
An unsatisfactory approach to increasing the frequency range of a VCO includes utilizing band switching circuits. Adding and deleting capacitance or inductance for each desired band of operation can cause a shift in the oscillation frequency of the VCO. Problems with this technology include the need for more logic control circuits, increased design complexity, and signal degradation.
Thus, there is need for a single wide band VCO with linear tuning range that does not require extra logic control circuits and/or increased design complexity.
There is a need for the following embodiments. Of course, the invention is not limited to these embodiments.
According to an aspect of the invention, a method for operating a wide band voltage controlled oscillator comprises using a control voltage to tune the capacitance of at least one hybrid n+ and p+ gate-doped voltage variable capacitor of the wide band voltage controlled oscillator.
According to another aspect of the invention, a hybrid voltage variable capacitor includes a substrate, a well adjacent to the substrate, a first and second set of contact elements adjacent to the well, a first channel layer adjacent to the well and bound by the first set of contact elements, a first insulating layer adjacent to the first channel layer, a first electrode adjacent to the first insulating layer, a second channel layer adjacent to the well and bound by the second set of contact elements, a second insulating layer adjacent to the second channel layer, and a second electrode adjacent to the second insulating layer; a capacitance of said hybrid voltage variable capacitor varying as a function of a voltage applied to said first and second set of contact elements.
These, and other, embodiments of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating various embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many substitutions, modifications, additions and/or rearrangements may be made within the scope of the invention without departing from the spirit thereof, and the invention includes all such substitutions, modifications, additions and/or rearrangements.